1. Field of the Invention
This invention relates to a zero thermal expansion material and a practical component part making use of the same, which are used in electronic materials, precision machine component parts, structural materials and so forth of products making use of high frequencies.
2. Description of the Prior Art
Electronic materials and structural materials have conventionally been produced using oxides and resins or using glass and metals. For example, substrates for high-frequency circuits have been produced using dielectrics or resins which have been made into sheets or plates. Such conventional electronic materials and structural materials usually have positive coefficients of thermal expansion. Hence, these materials have properties of causing expansion and contraction in accordance with rise and drop of ambient temperature.
Meanwhile, in recent years, materials whose coefficients of thermal expansion are negative in some crystal systems are reported. For example, in Chemi. Mater., 1995, 7, 412-417, K. Korthuis et al. reports ZrV2O7. In Chemi. Mater., 8, 1996, 2809-2823, J. S. O. Evans et al. reports ZrW2O8 and HfW2O8. In Pysica B 241-243 (1998) 311-316, the same J. S. O. Evans et al. reports materials having the general formula: A2(MO4)3 (A is Al, Y or a lanthanum group element), in particular, materials wherein A is Sc. In Journal of Solid-State Chemistry, 149, 92-98 (2000), D. A. Woodcock et al. also reports materials having the general formula: A2(MO4)3) (A is Al, Y or a lanthanum group element), in particular, materials wherein A is Y or Al.
Of these, Evans et al. asserts negative thermal expansion theory that, in materials having negative coefficients of thermal expansion, the whole bonding distance contracts because rotary motion increases with a rise in temperature, in an Mxe2x80x94Oxe2x80x94M (M is a metallic element) bond.
As these reports have been made, it has been studied to materialize a material having a low absolute value of coefficient of thermal expansion (a low thermal expansion material), using a mixture of a material having a positive coefficient of thermal expansion and the material having a negative coefficient of thermal expansion as in the foregoing. For example, Sleight et al.""s U.S. Pat. Nos. 5,322,559 and 5,433,778 disclose low thermal expansion materials comprised of a composite material of the above negative thermal expansion material and an epoxy resin.
However, it has not been reported that a method of producing such a material is applied to ceramic materials used widely in, e.g., high-frequency circuit component parts and the negative thermal expansion material and a ceramic material are simultaneously fired to produce a new low thermal expansion material.
Thus, conventional electronic materials or component parts and structural materials, which have positive coefficients of thermal expansion, inevitably cause expansion and contraction in accordance with changes in ambient temperature. Even a slight error in size thus caused inevitably brings about a great lowering of performance in the case of electronic materials, precision machine component parts and so forth used in high-frequency circuit component parts. Hence, such materials have had problems that not only any high working precision cannot be achieved but also electric and electronic properties tend to deteriorate.
More specifically, in such electronic materials or component parts, precision machine component parts and structural materials, not only a high working precision is required, but also, at the stage of production, the coefficient of thermal expansion must be controlled in accordance with use environment.
In addition, where materials free of any expansion and contraction in a high-temperature condition are demanded, there has been a problem that the composite material comprised of an epoxy resin and a negative thermal expansion material as reported by Sleight et al. can not substantially materialize such materials.
More specifically, in the field of precision machines in which the working precision is required in the order of microns, the above composite material can not cope with its use in a high-temperature condition. Accordingly, it is sought to provide structural materials and precision machine component parts making use of a material substantially free of any expansion and contraction over a wide temperature range.
An object of the present invention is to provide a material whose coefficient of thermal expansion is substantially zero over a wide temperature range (a zero thermal expansion material), and also to provide various materials and component parts making use of this materials and having good properties.
To achieve the above object, the present invention provides a zero thermal expansion material comprising a mixed material of a negative thermal expansion material and a positive thermal expansion material;
the negative thermal expansion material comprising a double oxide containing at least partly a compound represented by the chemical formula: RQ2O8 (wherein R is Zr, Hf or a tetravalent metallic element represented by a mixture system of these, and Q is a hexavalent metallic element selected from W and Mo); and the positive thermal expansion material comprising a material containing at least partly a compound represented by the chemical formula: MQX4 (wherein M is Mg, Ca, Sr, Ba, Ra or a divalent metallic element represented by a mixture system of any of these, Q is a hexavalent metallic element selected from W and Mo, and X is an element selected from O and S).
The present invention also provides a zero thermal expansion material comprising a double oxide represented by the chemical formula: (RM)(QO4)3 (wherein R is Zr, Hf or a tetravalent metallic element represented by a mixture system of these, M is Mg, Ca, Sr, Ba, Ra or a divalent metallic element represented by a mixture system of any of these, and Q is a hexavalent metallic element selected from W and Mo).
The present invention enables production of a zero thermal expansion material whose coefficient of thermal expansion is substantially zero. Since a ceramic material is used as the positive thermal expansion material, the coefficient of thermal expansion may little change even at a high temperature of 1,000xc2x0 C. or more. This makes it possible to provide a zero thermal expansion material which is a heat-resistant material also having a high working precision.
The present invention still also provides a practical component part making use of any of these zero thermal expansion materials, which more specifically includes high-frequency circuit substrates, high-frequency circuit component parts, precision machine component parts and structural materials.
Thus, when high frequencies in the millimeter wave range are used where, e.g., a component part has a length corresponding to wavelength at most, it is possible to actually provide electronic materials having a high-precision workability and also having a substantially zero coefficient of thermal expansion, and high-performance electronic component parts which may undergo less variations in characteristics due to temperature. In the filed of precision machines for which working precision is required in the order of microns, it is possible to provide good structural material and precision machine component parts substantially free of any expansion and contraction over a wide temperature range.